This invention relates to devices for coupling a torque driver to a fastener, and more particularly to devices which enable torque from the torque driver to be delivered to a fastener, and for reaction torque from the driver housing to be transmitted to the workpiece.
Large mechanical systems, such as airplanes, often require the use of large threaded fasteners tightened to high torque values, on the order of 350 to 750 foot pounds or higher. Traditionally, these large threaded fasteners have been tightened with the use of a long-handled torque wrench, typically five feet long. The process requires one operator to hold the socket on the fastener and another operator to apply power to the torque wrench by grasping the end of the socket wrench handle and pulling to exert the required torque on the fastener. Normally, the torquing operator can apply only a quarter of a turn or so before he must ratchet the wrench back to its original starting position to apply the next quarter turn. Since the breaking torque is always greater than the dynamic torque, it is the usual experience for the operators to reach the specified torque for that fastener at the beginning of one of the quarter turns. Thus, the actual dynamic torque to the fastener is often somewhat less than that specified by the design.
In certain critical fastening connections, it is necessary to have quality monitors present at the torquing operation to verify that the fasteners are properly torqued, and to gather data used in statistical process control. For those operations, an additional person is required to perform those functions. The use of two or three operators to do the job is thus wasteful of manpower and thereby increases the manufacturing cost.
Use of the hand operated, long-handled torque wrench is a physically taxing and difficult task. It is often operated from a sitting position wherein the operator braces his feet against a convenient foot hold on the floor and reaches forward between his legs with his arms to grasp the handle of the torque wrench, and then pulls the wrench toward him. In other applications, the operator may be required to stand in an awkward position, reaching over equipment that cannot be moved, or in an unbalanced position. These are all strained positions for the operator and risk injury which could cause increased delay and cost in the manufacturing process and personal inconvenience and suffering to the workers.
The concept of "joint relaxation", wherein the torque on a fastener in a joint decreases in the first minute or so after it has been fastened, increases the effort and time required to properly torque the fasteners, because there is no certain indication whether the joint has "relaxed", so the nuts must all be retorqued after several minutes following the initial torquing to ensure that they are at the specified torque.
Naturally, some considerable attention has been applied to improving the process of torquing large fasteners in the manufacture of large mechanical systems Impact wrenches have been studied, but they are noisy, difficult to calibrate, and incapable of delivering the required high torque at the necessary precision. The best solution to date has been the use of a pneumatic or electrical nut driver operating through a torque multiplier fastened to the workpiece. In that arrangement, the torque multiplier is bolted to a separate reaction plate that, in turn, is bolted to the workpiece over the fastener to be torqued, thereby providing a path for transmission of reaction torque exerted by the housing of the torque multiplier through the reaction plate to the workpiece.
This improved process is far superior to the hand operated, long-handled torque wrench in that it can be accomplished by one operator and does not require the use of a manually operated torque wrench. However, it does require a precisely machined reaction plate having a precisely machined hexagonal hole positioned precisely on the reaction plate over the position that will be occupied by the fastener when the reaction plate is bolted to the workpiece. Even with careful machining, the alignment of the torque multiplier with the fastener when the torque multiplier is inserted in the hexagonal hole and bolted to the plate is difficult. In addition, the torque multiplier must be hand held on the reaction plate with one hand while the the screws are inserted from the back side of the reaction plate with the other hand to secure the torque multiplier to the reaction plate. Another difficulty is the placement of the socket on the nut, because the nut may not be visible to the operator, so he must do it by feel. Finally, the torque multiplier must be unbolted and rebolted to the reaction plate for each nut to be tightened because the consequences of an unbolted reaction plate springing loose under high torque loads could be very severe. The bolting and unbolting of a reaction plate for every nut is a time consuming and annoyingly repetitive task.
Thus, there has long been a need in the art for a device for attaching a power operated torque multiplier to a workpiece, which device can be easily attached and detached in a simple, fast and easy motion, and wherein the socket on the drive rod of the torque multiplier can be fitted over the nut in full view of the operator, and without the necessity of simultaneously supporting the heavy torque multiplier with one hand while attempting to align the socket with the nut with the other hand.